The present invention concerns a threshing mechanism in which a threshing cylinder cooperates with an open concave and particularly with means for at least partially closing the concave by the attachment of one or more filler strips.
The typical concave used with a rasp bar threshing cylinder consists essentially of an arcuate grate, roughly concentric with the threshing cylinder. It is made up of spaced bars parallel to the axis of the cylinder and, threaded through the bars, a series of rods extending circumferentially and roughly concentric with the cylinder and inset somewhat below the inner edges of the axial bars. Thus, between each pair of neighboring axial bars, there is a narrow elongated recess extending the length of the cylinder with its fore-and-aft walls defined by the inner edges of the concave bars and a floor defined by the concave rods passing circumferentially through the bars.
In some crops and operations, it is desirable to close or partially close the concave so as to modify its threshing and separating action. This is commonly done by securing filler strips in the recesses, generally using the circumferential concave rods as anchoring means. The basic design of the conventional rasp bar cylinder and threshing concave is very old but patents disclosing means for modifying the concave characteristics, including means for closing or partially closing the concave continue to appear, suggesting that the cylinder/concave system is far from being optimized. Certainly the known methods of concave filler strip attachment have readily recognizable short comings. For example, Lindgren (U.S. Pat. No. 2,159,664) requires the modification of side bars of the concave (adding pins to help retain the filler strip) and relies on a fastening means which requires access from both the inner and outer sides of the concave.
Young (U.S. Pat. No. 2,686,523) relies on spring clips engaging the concave rods for strip retention. Although this method has had some success, it is still possible, in some operating conditions, for the spring clips to lose their grip and for a filler strip and join the downstream material flow, possibly with some damage to combine components.
Morgan's purpose (U.S. Pat. No. 3,092,115) is to provide a resilient surface for the concave but the method is still to provide "filler" strips, anchored between the concave's axial bars. Threaded studs extend from the underside of the filler strips through and between the circumferential concave rods which are spaced closely enough that a nut and flat washer can be used to secure the strips. However, retaining nuts in such locations are generally inaccessible and difficult to keep tight given the typical vibration of the concave during threshing operation.
In an effort to simplify attachment and reduce the risk of loose parts damaging the combine, Baumeister et al (U.S. Pat. No. 3,191,607) propose a compound strip assembly with opposing sets of hooks at its opposite ends, for hooking over the concave rods and being retained by axial elasticity in the filler strip assembly. Installation appears to be simple and convenient but the construction is more costly and results in an uneven filler strip surface and the reliability of retention is doubtful, certainly after extended service life.
Davidow et al (U.S. Pat. No. 3,439,684) also suggest a compound filler strip which is simple and convenient to install but lacks positive anchoring to the concave rods. In assembly, the filler bar is an inverted channel with the channel walls notched to match the concave rod spacing and a magnetic strip attached to the inner floor of the channel. This form of construction results in a certain minimum radial thickness of filler bar which may be greater than desirable in some applications. Certainly the risk of detachment and loss of the filler bar would be increased in concaves where the filler bar projected radially above the concaves axial bars.